In conventional correlation radar systems employing a coded sequence for range gating, echoes are selected throughout the range scale of the radar by correlating the delayed return echo code with an identical matched delayed reference code. Typically, such systems require the use of a large number of delay elements. When a target is at a given range R, there is typically a reflected echo signal which will have undergone a round trip transit time of 2R/C seconds from the transmitter to the receiver where C is the velocity of propagation. By delaying the transmitted reference code by an amount of time equal to the transmitter to target to receiver propagation delay (neglecting component delays) and using the delayed reference code to demodulate the received waveform, a replica of the initial reference carrier will result. Sufficient delays must be included in the delay circuit so that the above-mentioned propagation delay can be reproduced. Thus, large numbers of delay elements are required, the delay elements, of course, being dependent upon the length of the code utilized.
In order to overcome 5, attendant disadvantages of prior art correlation radar systems, the present invention utilizes a switching system wherein the number of delay elements required for the correlation testing throughout the range scale is reduced. By switching the physical placement of a delay in the correlation radar system, a dual range correlating capability is provided with a minimized number of delay elements.
The advantages of this invention, both as to its construction and mode of operation will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.